Proper: A chemistry term used to describe the transfer of electrons and subsequent bonding of a neucleophile to the back face of a molecule. The back side described is the chiral center, with subsistents in a tetrahedral formation facing away from the nucleophile. Once the backside attack is complete, the stereochemistry of the molecule is inverted.

chem eng slang: A difficult academic situation. It is often used to describe the difficulty of an assignment or a test. Synonymous with ass rape.

Term used for the attachment of the nucleophile in an SN2 reaction to kick off the leaving group. In slang, it means to fail a test or have a lot of difficulty on a test, especially an organic chemistry test.